Golf balls traditionally have been categorized in three different groups, namely, as one piece balls, two piece solid balls, and wound balls.
The one piece ball typically is formed from a solid mass of moldable material which has been cured to develop the necessary degree of hardness. It possesses no significant difference in composition between the interior and exterior of the ball. These balls do not have an enclosing cover. One piece balls are described, for example, in U.S. Pat. No. 3,313,545; U.S. Pat. No. 3,373,123; and U.S. Pat. No. 3,384,612.
The wound ball is made with a vulcanized rubber thread wound under tension around a solid or semi-solid core and thereafter enclosed in a single or multilayer covering of tough protective material. While for many years the wound ball satisfied the standards of both the U.S.G.A. and most golfers, it has several disadvantages. For example, a wound ball is difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity, rebound, "click", "feel", and the like.
Conventional multi-piece solid golf balls, on the other hand, include a solid resilient core having single or multiple cover layers employing different types of material molded on the core. The one piece golf ball and the solid core for a multi-piece solid (nonwound) ball frequently are formed from a combination of materials such as polybutadiene and other rubbers cross linked with zinc diacrylate or zinc dimethacrylate, and containing fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. For multi-piece nonwound golf balls, the cover typically contains a substantial quantity of ionomeric resins that impart toughness and cut resistance to the covers.
A number of multi-piece solid balls have been produced to address various needs of the industry. The different types of materials used to formulate the cores, covers, etc. of these balls dramatically alter the balls' overall characteristics. Various structures have been suggested using multi-layer cores and single layer covers wherein the core layers have different physical characteristics. For example, U.S. Pat. Nos. 4,714,253; 4,863,167; and 5,184,828 relate to three piece solid golf balls having improved rebound characteristics in order to increase flight distance. The '253 patent is directed towards differences in the hardness of the different layers. The '167 patent relates to a golf ball having a center portion and an outer layer containing a gravity filler such as tungsten or tungsten carbide so as to impart a higher specific gravity to the outer layer than that of the inner layer. Preferably, the outer layer is harder than the center portion. The '828 patent suggests that the maximum hardness must be located at the interface between the core and the mantle, and the hardness must then decrease both inwardly and outwardly.
A number of patents suggest improving the spin and feel by manipulating the core construction. For example, U.S. Pat. No. 4,625,964 relates to a solid golf ball having a core diameter not more than 32 mm and an outer layer having a specific gravity less than that of the core. In U.S. Pat. No. 4,650,193, it is suggested that a curable core elastomer be treated with a cure altering agent to soften an outer layer of the core. U.S. Pat. No. 5,002,281 is directed towards a three piece solid golf ball which has an inner core having a gravity greater than 1.0 but less than or equal to that of the outer shell which must be less than 1.3. U.S. Pat. Nos. 4,848,707 and 5,072,944 disclose three-piece solid golf balls having center and outer layers of different hardness. Other examples of such dual layer cores can be found in the following patents: U.S. Pat. No. 4,781,383; U.S. Pat. No. 4,858,924; U.S. Pat. No. 5,002,281; U.S. Pat. No. 5,048,838; U.S. Pat. No. 5,104,126; U.S. Pat. No. 5,273,286; U.S. Pat. No. 5,482,285; and U.S. Pat. No. 5,490,674.
Most professional golfers and good amateur golfers desire a golf ball that provides distance when hit off a driver, control and stopping ability on full iron shots, and high spin for short "touch and feel" shots. Many conventional two piece and thread wound performance golf balls have undesirable high spin rates on full shots. The excessive spin on full shots is a sacrifice made in order to achieve more spin on the shorter touch shots.
The multi-piece nonwound balls typically provide low deformation upon impact and a small contact area between the ball and the club face. This provides a greater degree of slipperiness on the club face and, therefore, less control over the ball and greater difficulty in stopping the ball on the green when using short irons. At least some of these deficiencies are considered to result also from a large moment of inertia exhibited by the multi piece balls. It would be useful to develop a ball with a controlled moment of inertia in order to provide the desired backspin when using short irons, but at the same time without adversely impacting the desired flight and roll distance of the ball when using a driver.
Prior artisans have attempted to incorporate spherical metal components in golf balls. For instance, U.S. Pat. No. 5,104,126 attempts to concentrate the weight of the golf ball in the center core region by utilizing a metal ball as the core component. However, that golf ball utilizes a single cover layer construction and admittedly conventional materials and structure. Various patents have been issued directed to game balls and practice balls containing metal centers, for instance U.S. Pat. Nos. 4,886,275 and 4,995,613. And, a rather old and dated patent to Harkins describes a golf ball containing a steel sphere. None of these patents however are capable of satisfying the needs and requirements of the current golf industry. Accordingly, there is a need for an improved golf ball, utilizing present state-of-the-art materials, configuration, and construction techniques.